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Hello. I had taken a hiatus from working on my '37 120 but am now returning to it. The first problem is that when attempting to start it, the motor turns slowly for about three revolutions and then stops. I was wondering if any of you out there had any bright ideas on how to locate the problem. Quite some time ago it would turn quickly enough to fire off the engine but not now. I have some ideas of my own, but would like to hear what else might be out there.
I will be asking more for your expertise as I get further along.
Thanks.

What is the battery voltage without load, and how old is it?

Did you try to charge it with a 6V battery charger?

Sound like the what I just when thru
A generator rebuild and a guy that knows how to diamond file the contacts in the voltage regulator solved the problem. He stated that the voltage regulator has a two step charging and the high amp mode was not working. It would let the battery recover after long periods of cranking. He rebuilt the generator (cut the commutator and new brushes) since it was out of the car. My voltage regulator is on top of the generator on 36 yours on the firewall on the 37. Just returned a NOS 37 voltage regulator to Max because it would not fit my car Still looking for a good voltage regulator
If you have a good fully charged battery, it should start but you will find that after long cranking, hard to start when you go to start it again
If the battery is good then you got other problems, check the ground or add another ground, that's were I would start
Seems to run good now
Just a thought
W

Sound like the what I just when thru
A generator rebuild and a guy that knows how to diamond file the contacts in the voltage regulator solved the problem. He stated that the voltage regulator has a two step charging and the high amp mode was not working. It would let the battery recover after long periods of cranking. He rebuilt the generator (cut the commutator and new brushes) since it was out of the car. My voltage regulator is on top of the generator on 36 yours on the firewall on the 37. Just returned a NOS 37 voltage regulator to Max because it would not fit my car Still looking for a good voltage regulator
If you have a good fully charged battery, it should start but you will find that after long cranking, hard to start when you go to start it again
If the battery is good then you got other problems, check the ground or add another ground, that's were I would start
Seems to run good now
Just a thought
W

In addition to the generator not charging resulting in a low battery, you could also have a failed cell in the battery or a cable connection which has oxidized. Cell failure and oxidation can happen overnight and can cause several symptoms depending on how much voltage or current is able to pass. The solenoid just clicking is a well known issue and example but slow cranking if the oxidation is not too severe can also be a symptom. Corrosion can be visible at a battery post and easily corrected at the terminal or other connection or it can be hidden inside the cable where the wire conductor is connected to the terminal. Internal issues usually cannot be satisfactorily repaired.

In addition to checking the nominal battery voltage which should be 6.3v at the terminals with the car just sitting, sometimes oxidation or corrosion will result in a h9gh enough resistance the terminal will get hot. If you can CAREFULLY feel the terminals, they should all be at ambient temperature. If one is warmer than the other that is suspect. You can often check for a failed cell by measuring the battery voltage at the terminals and then measure again while the headlights are on or the engine is trying to crank. The voltage should not drop much -- certainly less than a half a volt with lights on and no more than a volt when cranking. If there is a big drop, the battery is suspect.

It is doubtful the starter motor itself has an issue but that is a possibility which cannot be ruled out. Brush contact with the commutator could be bad and it is also possible a bushing is worn and has been slowing getting worse to the point the armature is finally dragging.